Hearing aid device



Dec. 16, 1941.

A. M. WENGEL I'IEARING AID DEVICE Filed April 15, 1940 2 Sheets-Sheet l n I 67: e;

Dec. 16, A. M. WENGEL HEARING AID DEVICE Filed April 15, 1940 2 Sheets-Sheet 2 I00 200 J00 /000 2000 0000 $00 lqvaa 0 :00 J00 1000 00a 6000 6270a mom:

I00, 200 00 1000 2000 @000 Java lqwa Patented Dec. 16, 1941 2,266,669 HEARING AID DEVICE -Arthur M. Wengel, Madison, Wis., assignor to Ray-O-Vac Company, a corporation of Wisconsin Application April 15, 1940, Serial No. 329,779

2 Claims.

This invention relates to a hearing aid device, and more particularly to binaural hearing aid apparatus for providing different corrections, as to average intensity and frequency-intensity characteristics, in each ear of the user of the device.

One feature of this invention is that it provides binaural hearing aid with simple and compact apparatus; another feature of this invention is that it provides independent correction for the two ears of the user; a further feature of this invention is that it enables the average intensity and the frequency-intensity characteristics of the sounds supplied to each ear from a single amplifier to be difierent; yet another feature of this invention is that it enables such independent binaural correction to be made with considerable simplicity, although in a circuit which is termed complex; other features and advantages of this invention will be apparent from the following specification and the drawings, in which:

Figure 1 is a circuit diagram of a hearing aid device embodying one form. of my invention; Figure 2 is a partial circuit diagram illustrating another form of my invention; Figure 3 is another partial circuit diagram illustrating still another form of my invention; Figure 4 is-a chart illustrative of the-intensity in difierent receivers when the circuit shown in Figure 1 is employed; Figure 5 is a chart illustrative of the sound intensity in the receivers under various conditions when the circuit partially illustrated in Figure 2 is employed; and Figure 6 is a chart illustrating the sound intensity in the two receivers when the circuit used in Figure 3 is employed.

It is highly desirable to take advantage of whatever residual hearing response there may cuit in such a way as to provide different compensation for each ear.

In conventional binaural hearing aid apparatus where a single microphone and amplifier are used the receivers are connected to its output in a simple circuit arrangement, with the tworeceivers in series across the output, or in parallel with respect to each other. In this case, of course, any frequency-intensity correction will be the same for each ear; and the average intensity I than a simple parallel or series arrangement, I

am enabled to secure any desired relation between the average sound intensity in the two cars. I am also able, within limits which are suflicient for all but very exceptional cases, to vary the slop or shape of the frequency-intensity characteristic curve of the sound supplied to one ear with respect to that supplied to the other.

In the particular form of my invention illustrated in Figure 1 I show, in circuit diagram'form,

' impulses corresponding a hearing aid device adapted to be worn on the person of the user. sound waves or impulses into electrical waves or thereto, and delivers these electrical impulses to a high gain amplifier.

bein both ears of a hard-of-hearing person; yet

possible to accomplish both of these desired results without the use of two separate amplifying means, resulting in a larger and heavier hearing aid device than is desirable for convenient wearing'or carrying on the person. I have devised apparatus which secures the desired results without the above-mentioned objection by using a single microphone and amplifier, with such gen- I eral correction incorporated in it as may be desir-able, and supplying its output to two carphones or receivers connected in a complex cir- This amplifier is here shown as comprising electronic tubes ll, l2 and I3 in cascade arrangement, with operative circuit connections therebetween. The specific details in this regard form no part of the present invention, since conventional resistance-coupled amplifier practice is followed. The input is, of course, delivered to the grid of the tube II; and the output of the amplifier taken from the plate of the tube [3.

In'order to provide desired general corrections as to output intensity and frequency-intensity relations with a given input, the amplifier includes volume and tone control means. The volume control means is here shownas the potentiometer ll, variations in the setting of this element resulting in variations in output intensity with a given input. A circuit coupling tube H to tube l2, moreover, includes two independent.

energy. dissipating branches. One of these dissipates energy to ground through a. condenser I5 A microphone It] converts,

and a variable resistance [6; and the other through a variable resistance i1 and a choke or inductance IS. The lower the resistance of the element IS the higherthe effective capacity of the condenser l5, and thus the more high frequency waves lost. The converse is true of the other branch circuit, as the inductance l8 tends to pass low frequency waves more easily than high frequency ones.

The plate of outputtube I3 .is connected to the positive voltage supply through an inductance I9; and is coupled to the receivers 20 and 2] through a condenser 22. While a conventional earphone symbol is used in the drawings, it will be understood that the receivers would in actual practice be as light and inconspicuous as possible. I have found, for example, a light crystal receiver, mounted on and carried by an ear portion adapted to be received by and frictionally retained in the ear recesses, to be particularly satisfactory. At any rate, there is only a single output current from the amplifier, and both receivers are energized by this current.

In the form of my invention illustrated in Figure 1 receiver 2| is in series with a parallel circuit having as one branch thereof the receiver 20 and as the other branch thereof an impedance element here shown as a resistance 23. This complex circuit results in a diflerent current fiow through receiver 2| than through receiver 20, and thus a difference in sound generated by the two receivers. This is illustrated in Figure 4. Assuming the general amplifier arrangement to be such as'to make its output curve substantially fiat, with only slightly more intensity in the high frequencies, receiver 2|, in the particular example tested, has afrequency-intensity curve identified as 24. The provision of a resistance in parallel with the receiver 20, however, not only changes its average intensity level, but also changes the slope of the curve. The use of a fifty thousand ohm resistance as the element 23 resulted, in the case of a given pair of receivers, in the receiver 20 having the frequency-intensity characteristic curve identified as 25. Changing this resistance to twenty-five thousand ohms resulted in the curve identified as 26. It will be readily seen that if one ear of the deaf person were particularly sensitive to low frequencies, with a chance of pain if these frequencies were of too high intensity, full advantage of the hearing response of the other car could be attained while protecting the sensitive ear from the low frequencies.

Another form of my invention is illustrated in Figure 2. Here the output of the amplifier is coupled, through the condenser 21, to a. complex circuit which comprises two parallel branches, one of which includes merely the receiver 28. The other branch comprises the receiver 29 in parallel with a resistance 30, both being in series with another resistance 3|. This arrangement is particularly satisfactory .where it is desired to deliver to the ear from the receiver 28 a sound I which rises in intensity with rising frequency;

and to deliver to the other ear from the receiver 29 a sound with a fairly fiat frequency-intensity characteristic, and of lower average intensity.

The results of using the circuit shown in Figure 2 in connection with a particular pair of receivers is illustrated in Figure 5. The frequencyintensity curve of the receiver 28 is here identifled as 32, while the three lower curves'represent the intensity at any given frequency in the receiver 29 with different values of resistors 30 and 3|.v Curve 33 represents the case where the resistance 30 has the value of one hundred thousand ohms and the resistance 3| 9. value of seventy-five thousand ohms; curve 34 represents the case when resistance 30 has a value of one hundred thousand ohms, as before, but resistance 31 has a value of only twenty-five thousand ohms; and curve 35 is illustrative of the response when resistance 30 has a value of twenty-five thousand ohms and resistance 3| a value of one hundred thousand ohms.

Figure 3 shows still another form in which my invention may be used. The coupling condenser,

36 in this case, has been found to be very satisfactory with a value of about,.05 'microfarad. In the circuit of Figure 3 receivers 31 and 38 are arranged in a complex circuit also including resistances 39 and 40 in a'manner similar to the I circuit of Figure 2. An additional circuit element is included, however, in the form of a condenser 4| shunting the inductance 42. In a given case, with this shunting condenser having a value of .005 microfarad receiver 31 had an intensity,- characteristic response curve identified as 43 in Figure 6; while the response curve of receiver 38 is indicated as 44. In all of these cases the zero level of the chart was chosen to correspond with .0015 mid. The impedance values used in the complex circuit would differ proportionately if receivers having different impedance values were used.

While I have described and shown certain embodiments of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims.

' I claim:

1. Binaural hearing aid apparatus for providing from a single source sounds which differ in average intensity and in frequency-intensity characteristics in each ear of the user from electrical impulses provided by a microphone and an amplifier generally correcting for the deficiencies of the particular user, including: a complex circuit connected to the output of the amplifier and including an inductive output load, two identical receivers-in shunt therewith, and a resistance element in shunt with one of said receivers only.

2. Apparatus of the character claimed in claim 1, wherein said receivers are of the type employing a piezo-electric crystal for the translation of electrical impulses into sound waves.

ARTHUR M. WENGEL. 

